Update postgres docs (#9989)

Author: richvdh

changelog.d/9988.doc

@@ -1 +1 @@
-Fix outdated minimum PostgreSQL version in postgres.md.
+Updates to the PostgreSQL documentation (`postgres.md`).

changelog.d/9989.doc

@@ -0,0 +1 @@
+Updates to the PostgreSQL documentation (`postgres.md`).

docs/postgres.md

@@ -33,28 +33,15 @@ Assuming your PostgreSQL database user is called `postgres`, first authenticate
     # Or, if your system uses sudo to get administrative rights
     sudo -u postgres bash
 
-Then, create a user ``synapse_user`` with:
+Then, create a postgres user and a database with:
 
+    # this will prompt for a password for the new user
     createuser --pwprompt synapse_user
 
-Before you can authenticate with the `synapse_user`, you must create a
-database that it can access. To create a database, first connect to the
-database with your database user:
+    createdb --encoding=UTF8 --locale=C --template=template0 --owner=synapse_user synapse
 
-    su - postgres # Or: sudo -u postgres bash
-    psql
-
-and then run:
-
-    CREATE DATABASE synapse
-     ENCODING 'UTF8'
-     LC_COLLATE='C'
-     LC_CTYPE='C'
-     template=template0
-     OWNER synapse_user;
-
-This would create an appropriate database named `synapse` owned by the
-`synapse_user` user (which must already have been created as above).
+The above will create a user called `synapse_user`, and a database called
+`synapse`.
 
 Note that the PostgreSQL database *must* have the correct encoding set
 (as shown above), otherwise it will not be able to store UTF8 strings.
@@ -63,79 +50,6 @@ You may need to enable password authentication so `synapse_user` can
 connect to the database. See
 <https://www.postgresql.org/docs/current/auth-pg-hba-conf.html>.
 
-If you get an error along the lines of `FATAL:  Ident authentication failed for
-user "synapse_user"`, you may need to use an authentication method other than
-`ident`:
-
-* If the `synapse_user` user has a password, add the password to the `database:`
-  section of `homeserver.yaml`. Then add the following to `pg_hba.conf`:
-
-  ```
-  host    synapse     synapse_user    ::1/128     md5  # or `scram-sha-256` instead of `md5` if you use that
-  ```
-
-* If the `synapse_user` user does not have a password, then a password doesn't
-  have to be added to `homeserver.yaml`. But the following does need to be added
-  to `pg_hba.conf`:
-
-  ```
-  host    synapse     synapse_user    ::1/128     trust
-  ```
-
-Note that line order matters in `pg_hba.conf`, so make sure that if you do add a
-new line, it is inserted before:
-
-```
-host    all         all             ::1/128     ident
-```
-
-### Fixing incorrect `COLLATE` or `CTYPE`
-
-Synapse will refuse to set up a new database if it has the wrong values of
-`COLLATE` and `CTYPE` set, and will log warnings on existing databases. Using
-different locales can cause issues if the locale library is updated from
-underneath the database, or if a different version of the locale is used on any
-replicas.
-
-The safest way to fix the issue is to take a dump and recreate the database with
-the correct `COLLATE` and `CTYPE` parameters (as shown above). It is also possible to change the
-parameters on a live database and run a `REINDEX` on the entire database,
-however extreme care must be taken to avoid database corruption.
-
-Note that the above may fail with an error about duplicate rows if corruption
-has already occurred, and such duplicate rows will need to be manually removed.
-
-
-## Fixing inconsistent sequences error
-
-Synapse uses Postgres sequences to generate IDs for various tables. A sequence
-and associated table can get out of sync if, for example, Synapse has been
-downgraded and then upgraded again.
-
-To fix the issue shut down Synapse (including any and all workers) and run the
-SQL command included in the error message. Once done Synapse should start
-successfully.
-
-
-## Tuning Postgres
-
-The default settings should be fine for most deployments. For larger
-scale deployments tuning some of the settings is recommended, details of
-which can be found at
-<https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server>.
-
-In particular, we've found tuning the following values helpful for
-performance:
-
--   `shared_buffers`
--   `effective_cache_size`
--   `work_mem`
--   `maintenance_work_mem`
--   `autovacuum_work_mem`
-
-Note that the appropriate values for those fields depend on the amount
-of free memory the database host has available.
-
 ## Synapse config
 
 When you are ready to start using PostgreSQL, edit the `database`
@@ -165,18 +79,42 @@ may block for an extended period while it waits for a response from the
 database server. Example values might be:
 
 ```yaml
-# seconds of inactivity after which TCP should send a keepalive message to the server
-keepalives_idle: 10
+database:
+  args:
+    # ... as above
+
+    # seconds of inactivity after which TCP should send a keepalive message to the server
+    keepalives_idle: 10
 
-# the number of seconds after which a TCP keepalive message that is not
-# acknowledged by the server should be retransmitted
-keepalives_interval: 10
+    # the number of seconds after which a TCP keepalive message that is not
+    # acknowledged by the server should be retransmitted
+    keepalives_interval: 10
 
-# the number of TCP keepalives that can be lost before the client's connection
-# to the server is considered dead
-keepalives_count: 3
+    # the number of TCP keepalives that can be lost before the client's connection
+    # to the server is considered dead
+    keepalives_count: 3
 ```
 
+## Tuning Postgres
+
+The default settings should be fine for most deployments. For larger
+scale deployments tuning some of the settings is recommended, details of
+which can be found at
+<https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server>.
+
+In particular, we've found tuning the following values helpful for
+performance:
+
+-   `shared_buffers`
+-   `effective_cache_size`
+-   `work_mem`
+-   `maintenance_work_mem`
+-   `autovacuum_work_mem`
+
+Note that the appropriate values for those fields depend on the amount
+of free memory the database host has available.
+
+
 ## Porting from SQLite
 
 ### Overview
@@ -185,9 +123,8 @@ The script `synapse_port_db` allows porting an existing synapse server
 backed by SQLite to using PostgreSQL. This is done in as a two phase
 process:
 
-1.  Copy the existing SQLite database to a separate location (while the
-    server is down) and running the port script against that offline
-    database.
+1.  Copy the existing SQLite database to a separate location and run
+    the port script against that offline database.
 2.  Shut down the server. Rerun the port script to port any data that
     has come in since taking the first snapshot. Restart server against
     the PostgreSQL database.
@@ -245,3 +182,60 @@ PostgreSQL database configuration file `homeserver-postgres.yaml`:
     ./synctl start
 
 Synapse should now be running against PostgreSQL.
+
+
+## Troubleshooting
+
+### Alternative auth methods
+
+If you get an error along the lines of `FATAL:  Ident authentication failed for
+user "synapse_user"`, you may need to use an authentication method other than
+`ident`:
+
+* If the `synapse_user` user has a password, add the password to the `database:`
+  section of `homeserver.yaml`. Then add the following to `pg_hba.conf`:
+
+  ```
+  host    synapse     synapse_user    ::1/128     md5  # or `scram-sha-256` instead of `md5` if you use that
+  ```
+
+* If the `synapse_user` user does not have a password, then a password doesn't
+  have to be added to `homeserver.yaml`. But the following does need to be added
+  to `pg_hba.conf`:
+
+  ```
+  host    synapse     synapse_user    ::1/128     trust
+  ```
+
+Note that line order matters in `pg_hba.conf`, so make sure that if you do add a
+new line, it is inserted before:
+
+```
+host    all         all             ::1/128     ident
+```
+
+### Fixing incorrect `COLLATE` or `CTYPE`
+
+Synapse will refuse to set up a new database if it has the wrong values of
+`COLLATE` and `CTYPE` set, and will log warnings on existing databases. Using
+different locales can cause issues if the locale library is updated from
+underneath the database, or if a different version of the locale is used on any
+replicas.
+
+The safest way to fix the issue is to dump the database and recreate it with
+the correct locale parameter (as shown above). It is also possible to change the
+parameters on a live database and run a `REINDEX` on the entire database,
+however extreme care must be taken to avoid database corruption.
+
+Note that the above may fail with an error about duplicate rows if corruption
+has already occurred, and such duplicate rows will need to be manually removed.
+
+### Fixing inconsistent sequences error
+
+Synapse uses Postgres sequences to generate IDs for various tables. A sequence
+and associated table can get out of sync if, for example, Synapse has been
+downgraded and then upgraded again.
+
+To fix the issue shut down Synapse (including any and all workers) and run the
+SQL command included in the error message. Once done Synapse should start
+successfully.